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Lecture5Notes - Lecture 5 Polymer Solution Thermodynamics 1...

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Unformatted text preview: Lecture 5 Polymer Solution Thermodynamics 1 1 Wednesday, October 6, 2010 Excluded Volume Excluded volume describes the volume around a monomer from which another monomer is excluded A positive excluded volume means that repulsion occurs between monomers A negative excluded volume means that the monomers are attracted to each other When excluded volume equals zero, this is called the theta state and it describes an ideal chain v = 0 R~N 1/2 v < 0 R~N 1/3 v > 0 R~N 3/5 Monomers have some repulsion, resulting in a stretched chain Monomer-monomer repulsion is perfectly balanced by attraction Monomer-monomer attraction results in smaller coil Remember, this was our starting point 2 Excluded Volume Excluded volume describes the volume around a monomer from which another monomer is excluded A positive excluded volume means that repulsion occurs between monomers A negative excluded volume means that the monomers are attracted to each other When excluded volume equals zero, this is called the theta state and it describes an ideal chain v = 0 R~N 1/2 v < 0 R~N 1/3 v > 0 R~N 3/5 Monomers have some repulsion, resulting in a stretched chain Monomer-monomer repulsion is perfectly balanced by attraction Monomer-monomer attraction results in smaller coil Remember, this was our starting point 2 Wednesday, October 6, 2010 Course Overview 10-10 10 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 1 A 1 nm 1 + m 1 mm 1 cm 1 m atoms, bond lengths DNA, virus collagen tropohelix e. coli red blood cell capillaries small blood vessel critical size bone defect eyeball tooth organ person Lectures 5 and 6: Polymers mixing with other polymers, and polymers mixing with solvent 3 Wednesday, October 6, 2010 Todays Concepts Last time, we talked about the free energy of the chain in its environment, and how minimizing free energy drives chain conformation Today, we will talk about free energy of mixing Entropy favors mixing Enthalpy may or may not favor mixing Whether or not you get a homogenous mixture (solution) or phase separation will depend on the balance of entropy and enthalpy; depends on composition Well introduce a new term - - which is the Flory-Huggins interaction parameter. It is supposed to describe the enthalpy of mixing and is directly related to excluded volume. If theres time, well learn how to construct a phase diagram (and read one). 4 Wednesday, October 6, 2010 Entropy of Binary Mixing If you mix together two species, A and B to form a single phase, we often assume no overall volume change V A , the volume of species A, is mixed with V B , the volume of species B to make a mixture of volume V A +V B 5 V A V B V A +V B Wednesday, October 6, 2010 Entropy of Binary Mixing The mixture of A and B is macroscopically uniform and A and B randomly fill an entire lattice The volume fractions of the two components in the binary mixture are A and B A = V A V A + V B B = V B V A + V B = 1 A 6 Wednesday, October 6, 2010 Entropy of Binary Mixing...
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This note was uploaded on 11/29/2010 for the course BME 104 taught by Professor Kasko during the Fall '10 term at UCLA.

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Lecture5Notes - Lecture 5 Polymer Solution Thermodynamics 1...

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